1956 Citroën Patent “Improvement to vehicle suspension” — constant attitude via radar and magnetic memory

In this document

The problem posed

The memorandum opens with a classic observation: traditional elastic suspensions, by absorbing obstacles, cause “chassis movements” and “variations in wheel grip”, as well as periodic vibrations that are difficult to dampen p. 1-2.

The principle invented

The proposed solution consists of making the position of the wheels depend not only on gravity and elasticity, but on “internal forces of the vehicle”, organised to give each wheel the position ensuring a constant attitude of the chassis p. 2. The text mentions several possible forms of energy accumulator: mechanical, inertial, hydraulic, pneumatic, hydro-pneumatic, hydro-mechanical or electrical p. 2.

The detection and memory device

A “detector” records road irregularities ahead of each wheel: pilot wheel, or “echo interference sounder” using electromagnetic, ultrasonic or light waves p. 3. The patent describes recording these indications on a magnetic wire or disc, read with a delay depending on the vehicle's speed, in order to correct the inertia of the mechanism p. 4. A simpler variant directly uses hydraulic pressure variations in “feed-back” p. 3.

The detailed embodiment

Figure 1, described on pages 8-9, presents a wheel (1) connected to the chassis (2) by an articulated arm (3) and a piston (5) in a cylinder (6), supplied by a reservoir (7) pressurized by the engine (8), via a four-way spool valve (9). This valve is controlled by an electromagnetic wave transceiver described as a “radar” (11), whose signal, transformed by a transformer (12) and a coil (13), influences a magnetic wire (14) driven by pulleys (15-16) whose speed follows that of the vehicle, before acting on an electromagnet (20) controlling the valve p. 9.

Envisaged applications

The text extends the principle to motorcycles, trucks, all-terrain vehicles, but also to fast ships and hydrofoils on articulated floats, and to aircraft, where the invention would aim to make the device describe “a curve tangent to the ground” at the moment of landing p. 7-8.

Claims

Eight claims close the document p. 9-11, covering the general principle of constant-attitude suspension via servo-controlled internal forces (1), prior recording with variable-delay memory (2), the hydro-pneumatic embodiment (3), electromagnetic control via echo sounder (4-5), weighting according to speed (6), and non-road applications, including aeronautical (7-8).

Context

This patent is part of the research conducted at Citroën during the 1950s, which would lead to the hydro-pneumatic suspension equipping the DS presented in 1955. Paul Magès remains, in the history of the brand, the engineer associated with the principle.

The radar and magnetic recording mentioned here were, for the time, cutting-edge technologies; their association with an automotive suspension belongs more, historically, to patented foresight than to an immediate industrial implementation — the production DS would rely on simpler hydraulic regulation.

Archivist's perspective

This descriptive memorandum, dated 1956 by the handwritten annotation “1000/56” appearing at the top p. 1, testifies to a phase where the Citroën team was exploring very ambitious servo-control paths — up to the use of a radar and a magnetic memory — for attitude control.

It seems that this text corresponds to a variant or a more advanced conceptual extension than the hydro-pneumatic suspension actually marketed, notably through the use of prior recording of road irregularities p. 3-4 and the claimed extension to aircraft and ships (p. 7-8, claims 7-8).

The handwritten correction adding the word “servo-” before “control” p. 10-11 suggests a careful proofreading of the text at the time of filing, specifying the technical terminology used.

The diagram corresponding to this mechanism can be consulted in the patent 1000/56 drawing sheet, which illustrates the numbered elements described on pages 8-9 (wheel, piston, valve, radar, magnetic wire).